Systems under consideration normally comprise miniature electronic apparatus including means for detecting abnormal tire pressure as well as sensing means for detecting trailer wheel bearing temperature.
One example of miniaturized electronic apparatus for detecting malfunction from a source on a vehicle is that disclosed in U.S. Pat. No. 3,491,335.
U.S. Pat. No. 3,491,335, discloses a temperature detection system wherein a temperature sensor controls a transmitter that emits a signal to a remote receiver upon detecting excessive heat, activating a warning device.
U.S. Pat. No. 3,491,335 further discloses the use of a temperature sensor which can be utilized to energize a transmitter that emits a radio frequency signal to a remote receiver for activation of a warning device.
Particularly, U.S. Pat. No. 3,491,335 utilizes a bi-metallic sensor which moves in accordance with the temperature on the wheel to which it is attached to close, respectively, a primary circuit and a secondary circuit which causes the transmitter to be energized and emit a signal. Closing of the primary circuit energizes the transmitter to emit a signal at a given predetermined frequency. As the temperature sensed increases the bi-metallic sensor causes the secondary circuit to be closed which energizes a subcarrier oscillator to modulate the signal and algebraically add the frequencies of the transmitter signal. The receiver at a remote location from the transmitter accepts the signal and, when only moderate temperatures have been sensed at the wheel of the vehicle, the receiver activates a warning light. When excessive temperatures are encountered the secondary circuit is closed and the receiver picks up the modulated signal and activates a warning speaker.
Another example of warning or alarm systems for vehicles includes U.S. Pat. No. 3,380,021, which discloses tire pressure and wheel bearing indicators in combination and includes means for indicating to the operator of the vehicle the tire pressure and wheel bearing temperature.
All of the prior alternatives, however, require, particularly in the case of vehicles such as tractor trailers, extensive modification to the axles to install the device making them impractical to add on for use with existing vehicles.
Further, in the case of vehicles such as tractor trailers installation at the time of manufacture would not benefit the operators of the great many tractor trailers presently in use worldwide. Further, it is the nature of tractor trailer operators to distrust any apparatus which would require extensive modification to the vehicle to be installed.
This invention overcomes the disadvantages of the prior art without requiring, as in the case of tractor trailers, extensive modification to existing vehicles presently in the marketplace as will hereinafter become clear upon reading description of the preferred embodiment of the invention.